How should I correctly use setState for the following object

If I have the following object in state. What is the correct way to write a setState function to update formList[1].name from "Name2" to "New Name"? Each of these fields are linked to an input field.

state = {
  formList = {
    0 : {
      id: 10,
      name: "Name1",
      date: "11/27/2019"
    },
    1 : {
      id: 11,
      name: "Name2",
      date: "11/27/2019"
    }
  }
}

I tried the below. Where for my example above, index is passed 1 and field is passed "name". I would like to keep the field name dynamic so that I could use this for all input fields

METHOD 1

updateForm = (e, index, field) => {
  const newValue = e.target.value;
  this.setState((prevState) => {
    return {
      edittedDataList: {
        ...prevState.edittedDataList,
        [prevState.edittedDataList[index][field]]: newValue
      }
    }
  })
}

But whenever I start typing into the name input field, my state changes to the below

RESULT 1

state = {
  formList = {
    0 : {
      id: 10,
      name: "Name1",
      date: "11/27/2019"
    },
    1 : {
      id: 11,
      name: "Name2",
      date: "11/27/2019"
    },
    Name2: "Name21" // where 1 is the character I pressed
  }
}

I also tried setting state using the below. It actually works with setting the state but I believe it may mutate the state so I don't think it is the correct way to setState. It also has a weird side effect

METHOD 2

updateForm = (e, index, field) => {
  const newValue = e.target.value;
  this.setState((prevState) => {
    return prevState.edittedDataList[editAtIndex][field] = newValue;
  })
}

RESULT 2

state = {
  0: "N",
  1: "e",
  2: "w",
  3: " ",
  4: "N",
  5: "a",
  6: "m",
  7: "e",
  formList = {
    0 : {
      id: 10,
      name: "Name1",
      date: "11/27/2019"
    },
    1 : {
      id: 11,
      name: "New Name",
      date: "11/27/2019"
    }
  }
}

Can someone show me the correct way to write setState and explain why my current setState functions are having strange results?

Thanks in advance